Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$144.43	4.827%	$151.4016	$151.40	$151.40	$151.40
Purchase #2	$184.60	3.656%	$191.349	$191.35	$191.35	$191.30
Purchase #3	$216.30	11.158%	$240.4348	$240.43	$240.45	$240.40
Purchase #4	$123.79	12.632%	$139.4272	$139.43	$139.45	$139.40
Purchase #5	$61.33	5.396%	$64.6394	$64.64	$64.65	$64.60
Purchase #6	$41.35	8.299%	$44.7816	$44.78	$44.80	$44.80
Purchase #7	$160.81	8.454%	$174.4049	$174.40	$174.40	$174.40
7 purchase totals =	$932.61		$1,006.4385	$1,006.43	$1,006.50	$1,006.30